1. Field of the Invention
This invention relates to a method for formation of an amorphous or crystalline functional thin film such as semiconductor film, insulating film, conductive film, etc., particularly a deposited film which is useful for uses such as active or passive semiconductor device, photosemiconductive device or photosensitive device for solar battery or electrophotography etc.
2. Related Background Art
For formation of deposited films, there have been attempted the vacuum vapor deposition method, the plasma CVD method, the thermal CVD method, the optical CVD method, the reactive sputtering method, the ion plating method, etc. Generally, the plasma CVD method has been widely used and industrialized.
However, the deposited films obtained according to these methods for formation of deposited films have been demanded to be applied for electronic devices or photoelectronic devices for which higher functions are demanded, and therefore there is room left for improvement of further improvement of overall characteristics with respect to electrical and optical characteristics, and fatigue characteristic or use environmental characteristic in repeated use, and further productivity, bulk productivity, including uniformness, reproducibility, etc.
The reaction process in formation of a deposited film according to the plasma CVD method which has been generalized in the prior art is considerably complicated as compared with the thermal CVD method of the prior art, and its reaction mechanism involves not a few ambiguous points. Also, there are a large number of parameters for formation of a deposited film (for example, substrate temperature, flow rate and flow rate ratio of the introduced gases, pressure during formation, high frequency power, electrode structure, structure of the reaction vessel, speed of evacuation, plasma generating system, etc.). Because of the combination of such a large number of parameters, the plasma may sometimes become unstable state, whereby marked deleterious influences were exerted frequently on the deposited film formed. Besides, the parameters characteristic of the device must be selected for each device and therefore under the present situation it has been difficult to generalize the production conditions.
Among them, for example, in the case of the group III-V compound semiconductor film, with respect to exhibiting sufficiently satisfactory electric and optical characteristics for respective uses, it has been proposed to form it according to the plasma CVD method.
However, depending on the application use of the deposited film, bulk production having reproducibility must be attempted with full satisfaction of enlargement of area, uniformity of film thickness as well as uniformity of film quality, and therefore in formation of a deposited film according to the plasma CVD method, enormous installation investment is required for a bulk production device and also management items for such bulk production become complicated, with a width of management tolerance being narrow and the control of the device being severe. These are pointed as the problems to be improved in the future.
On the other hand, according to the technique of the prior art by conventional CVD method, high temperature is required and a deposited film having satisfactory characteristics on industrial level could not necessarily be obtained.
These remain to be greater problems particularly in the case of forming a thin deposited film of the group III-V compounds.
As described above, in formation of functional films, it has been earnestly desired to develop a method for forming a deposited film which is capable of bulk production by means of a device of low cost, while maintaining the characteristics as well as uniformity which are practicably available.